android: extend support for protocol navigation to Android

Extends support for the `navigate` path of the `tailscale:` protocol to Android,
mirroring the existing macOS routes & pending iOS routes.

All settings tabs without existing routes simply open the main settings view
for now.

```
tailscale://navigate/main/devices
tailscale://navigate/main/devices/<computedName or stableID>
tailscale://navigate/main/exit-nodes
tailscale://navigate/main/exit-nodes/<stableID>
tailscale://navigate/main/exit-nodes/location/<country>
tailscale://navigate/settings[/<anyTab>]
```

The `scripts/deeplink-probe.sh` script can be used to trigger the application to
navigate to a given route by passing that to it.
e.g., `./tool/go run ./scripts/deeplink-probe.go main/devices`

updates tailscale/corp#41056

Signed-off-by: Will Hannah <willh@tailscale.com>

Author: willh-ts

.gitignore

@@ -51,3 +51,6 @@ libtailscale-sources.jar
 .DS_Store
 
 tailscale.version
+
+# .tmp folder
+.tmp/

android/src/main/AndroidManifest.xml

@@ -57,6 +57,12 @@
             <intent-filter>
                 <action android:name="android.service.quicksettings.action.QS_TILE_PREFERENCES" />
             </intent-filter>
+            <intent-filter>
+                <action android:name="android.intent.action.VIEW" />
+                <category android:name="android.intent.category.DEFAULT" />
+                <category android:name="android.intent.category.BROWSABLE" />
+                <data android:scheme="tailscale" android:host="navigate" />
+            </intent-filter>
         </activity>
         <activity
             android:name="ShareActivity"

android/src/main/java/com/tailscale/ipn/MainActivity.kt

@@ -62,6 +62,7 @@ import com.tailscale.ipn.ui.model.Ipn
 import com.tailscale.ipn.ui.notifier.Notifier
 import com.tailscale.ipn.ui.theme.AppTheme
 import com.tailscale.ipn.ui.util.AndroidTVUtil
+import com.tailscale.ipn.ui.util.DeepLinkNavigator
 import com.tailscale.ipn.ui.util.set
 import com.tailscale.ipn.ui.util.universalFit
 import com.tailscale.ipn.ui.view.AboutView
@@ -114,6 +115,8 @@ class MainActivity : ComponentActivity() {
   private lateinit var vpnPermissionLauncher: ActivityResultLauncher<Intent>
   private lateinit var appViewModel: AppViewModel
   private lateinit var viewModel: MainViewModel
+  private var deepLinkNavigator: DeepLinkNavigator? = null
+  private var pendingDeepLink: Uri? = null
 
   val permissionsViewModel: PermissionsViewModel by viewModels()
 
@@ -136,6 +139,8 @@ class MainActivity : ComponentActivity() {
   override fun onCreate(savedInstanceState: Bundle?) {
     super.onCreate(savedInstanceState)
 
+    pendingDeepLink = deepLinkUri(intent)
+
     // grab app to make sure it initializes
     App.get()
     appViewModel = (application as App).getAppScopedViewModel()
@@ -253,6 +258,17 @@ class MainActivity : ComponentActivity() {
 
       navController = rememberNavController()
 
+      LaunchedEffect(navController) {
+        val nav = DeepLinkNavigator(navController)
+        deepLinkNavigator = nav
+        pendingDeepLink?.let {
+          pendingDeepLink = null
+          if (!nav.handle(it)) {
+            TSLog.d(TAG, "Deep link handler returned false for $it")
+          }
+        }
+      }
+
       AppTheme {
         Surface(color = MaterialTheme.colorScheme.inverseSurface) { // Background for the letterbox
           Surface(modifier = Modifier.universalFit()) { // Letterbox for AndroidTV
@@ -404,7 +420,9 @@ class MainActivity : ComponentActivity() {
                   }
                 }
             if (isIntroScreenViewedSet()) {
-              navController.navigate("intro")
+              if (pendingDeepLink == null) {
+                navController.navigate("intro")
+              }
               setIntroScreenViewed(true)
             }
           }
@@ -483,6 +501,23 @@ class MainActivity : ComponentActivity() {
         }
       }
     }
+    deepLinkUri(intent)?.let { uri ->
+      val nav = deepLinkNavigator
+      if (nav != null) {
+        if (!nav.handle(uri)) {
+          TSLog.d(TAG, "Deep link handler returned false for $uri")
+        }
+      } else {
+        pendingDeepLink = uri
+      }
+    }
+  }
+
+  private fun deepLinkUri(intent: Intent?): Uri? {
+    if (intent?.action != Intent.ACTION_VIEW) return null
+    val uri = intent.data ?: return null
+    if (uri.scheme != "tailscale" || uri.host != "navigate") return null
+    return uri
   }
 
   private fun login(urlString: String) {

android/src/main/java/com/tailscale/ipn/ui/util/DeepLinkNavigator.kt

@@ -0,0 +1,105 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+package com.tailscale.ipn.ui.util
+
+import android.net.Uri
+import androidx.navigation.NavHostController
+import com.tailscale.ipn.ui.model.Tailcfg
+import com.tailscale.ipn.ui.notifier.Notifier
+import com.tailscale.ipn.util.TSLog
+
+// Deep links must only navigate — never perform an action on the user's
+// behalf. Tails whose leaf would imply an action (e.g., a specific exit
+// node) are accepted for URL compatibility but resolve to the parent
+// view; the user picks and confirms in-app.
+class DeepLinkNavigator(private val navController: NavHostController) {
+  companion object {
+    private const val TAG = "DeepLinkNavigator"
+  }
+
+  fun handle(uri: Uri): Boolean {
+    if (uri.host != "navigate") return false
+    val segments = uri.pathSegments
+    val window = segments.firstOrNull() ?: return false
+    val tail = segments.drop(1)
+
+    return when (window) {
+      "main" -> handleMain(tail)
+      "settings" -> {
+        showSettings()
+        true
+      }
+      else -> false
+    }
+  }
+
+  private fun handleMain(tail: List<String>): Boolean {
+    val tab = tail.firstOrNull() ?: return false
+    val rest = tail.drop(1)
+
+    return when (tab) {
+      "devices" ->
+          when (rest.size) {
+            0 -> {
+              showDeviceList()
+              true
+            }
+            1 -> pushDeviceDetail(rest[0])
+            else -> false
+          }
+      "exit-nodes" ->
+          when {
+            rest.size <= 1 || (rest.size == 2 && rest[0] == "location") -> {
+              showExitNodePicker()
+              true
+            }
+            else -> false
+          }
+      else -> false
+    }
+  }
+
+  private fun showDeviceList() {
+    popToMain()
+  }
+
+  private fun pushDeviceDetail(identifier: String): Boolean {
+    val node = findNode(identifier)
+    if (node == null) {
+      TSLog.d(TAG, "Deep link: device not found for '$identifier'")
+      return false
+    }
+    navigateOverMain("peerDetails/${node.StableID}")
+    return true
+  }
+
+  private fun findNode(identifier: String): Tailcfg.Node? {
+    val netmap = Notifier.netmap.value ?: return null
+    val all = netmap.Peers.orEmpty() + netmap.SelfNode
+    return all.firstOrNull { identifier.equals(it.ComputedName, ignoreCase = true) }
+        ?: all.firstOrNull { it.StableID == identifier }
+  }
+
+  private fun showExitNodePicker() {
+    navigateOverMain("exitNodes")
+  }
+
+  private fun showSettings() {
+    navigateOverMain("settings")
+  }
+
+  private fun navigateOverMain(route: String) {
+    navController.navigate(route) {
+      popUpTo("main") { inclusive = false }
+      launchSingleTop = true
+    }
+  }
+
+  private fun popToMain() {
+    val popped = navController.popBackStack(route = "main", inclusive = false)
+    if (!popped) {
+      TSLog.d(TAG, "Deep link: popBackStack to 'main' returned false")
+    }
+  }
+}

scripts/deeplink-probe.go

@@ -0,0 +1,94 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Command deeplink-probe fires a tailscale://navigate/<path> URI at an
+// attached device three ways (BROWSABLE implicit, bare implicit, explicit
+// component) and tails the relevant logcat lines so you can confirm
+// DeepLinkNavigator saw the intent.
+package main
+
+import (
+	"bufio"
+	"flag"
+	"fmt"
+	"io"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+	"time"
+)
+
+const defaultPath = "main/devices"
+
+func main() {
+	flag.Usage = func() {
+		fmt.Fprintf(os.Stderr, "Usage: %s [path-after-navigate]\n", filepath.Base(os.Args[0]))
+		fmt.Fprintf(os.Stderr, "  default path: %s\n", defaultPath)
+	}
+	flag.Parse()
+
+	tail := defaultPath
+	if flag.NArg() >= 1 {
+		tail = flag.Arg(0)
+	}
+	uri := "tailscale://navigate/" + strings.TrimPrefix(tail, "/")
+
+	logPath := filepath.Join(os.TempDir(), "deeplink-probe.log")
+	logFile, err := os.Create(logPath)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "cannot create %s: %v\n", logPath, err)
+		os.Exit(1)
+	}
+	defer logFile.Close()
+
+	tee := io.MultiWriter(os.Stdout, logFile)
+
+	fmt.Printf("URI: %s\nLogging to %s\n\n", uri, logPath)
+
+	if err := exec.Command("adb", "logcat", "-c").Run(); err != nil {
+		fmt.Fprintf(os.Stderr, "adb logcat -c failed: %v\n", err)
+	}
+
+	fires := []struct {
+		label string
+		shell string
+	}{
+		{"implicit (BROWSABLE)", "am start -W -a android.intent.action.VIEW -c android.intent.category.BROWSABLE -d '" + uri + "'"},
+		{"implicit (no category)", "am start -W -a android.intent.action.VIEW -d '" + uri + "'"},
+		{"explicit component", "am start -W -n com.tailscale.ipn/.MainActivity -a android.intent.action.VIEW -d '" + uri + "'"},
+	}
+	for _, f := range fires {
+		fmt.Fprintf(tee, "=== %s ===\n", f.label)
+		cmd := exec.Command("adb", "shell", f.shell)
+		cmd.Stdout = tee
+		cmd.Stderr = tee
+		if err := cmd.Run(); err != nil {
+			fmt.Fprintf(tee, "adb failed: %v\n", err)
+		}
+		fmt.Fprintln(tee)
+	}
+
+	time.Sleep(time.Second)
+
+	fmt.Fprintln(tee, "\n=== logcat ===")
+	logCmd := exec.Command("adb", "logcat", "-d", "-v", "brief")
+	logCmd.Stderr = tee
+	logOut, err := logCmd.StdoutPipe()
+	if err != nil {
+		fmt.Fprintf(tee, "adb logcat pipe failed: %v\n", err)
+	} else if err := logCmd.Start(); err != nil {
+		fmt.Fprintf(tee, "adb logcat failed to start: %v\n", err)
+	} else {
+		scanner := bufio.NewScanner(logOut)
+		for scanner.Scan() {
+			line := scanner.Text()
+			if strings.Contains(line, "Main Activity") || strings.Contains(line, "DeepLinkNavigator") {
+				fmt.Fprintln(tee, line)
+			}
+		}
+		_ = logCmd.Wait()
+	}
+
+	fmt.Printf("\nFull output: %s\n", logPath)
+}